Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$118.29	8.364%	$128.1838	$128.18	$128.20	$128.20
Purchase #2	$157.42	9.387%	$172.197	$172.20	$172.20	$172.20
Purchase #3	$144.64	12.162%	$162.2311	$162.23	$162.25	$162.20
Purchase #4	$235.39	3.657%	$243.9982	$244.00	$244.00	$244.00
Purchase #5	$122.94	11.573%	$137.1678	$137.17	$137.15	$137.20
Purchase #6	$166.67	6.663%	$177.7752	$177.78	$177.80	$177.80
Purchase #7	$69.38	13.370%	$78.6561	$78.66	$78.65	$78.70
7 purchase totals =	$1,014.73		$1,100.2092	$1,100.22	$1,100.25	$1,100.30